The present invention relates to a vehicle navigational receiver module.
Conventional receiver modules may be used, for example, for receiving GPS navigational radio signals.
The number of radio services that are used in motor vehicles is steadily increasing, and the spectrum of radio frequencies that are used by these services is becoming wider and wider. The different frequencies of the services require antennas of different types of construction and dimensions, and mounting them on a vehicle is becoming increasingly problematic.
The navigational radio service GPS (Global Positioning System) works at a frequency of 1.57542 GHz; for receiving the signals of this service, active patch antennas are generally used, more precisely, microstrip antennas including remote-fed, low-noise amplifiers. A receiver module of this type may be mounted in the area of the vehicle skin so as to save space; the actual GPS receiver, in which the radio signals are evaluated and position information is determined, may be connected to this module by a long cable and may therefore be mounted anywhere in the vehicle.
Familiar as a telematic service for use in vehicles is the DSRC system (Dedicated Short Range Communications for Road Transport Telematics). It operates on a frequency of 5.8 GHz. It is used, for example, for the automated determination, or the electronic payment, of tolls.
DSRC transponders, so-called OBUs (On Board Units), are currently found mainly as small retrofitted units, that are mounted in the interior of a motor vehicle on the windshield. So as not to impair the visibility through the windshield, these transponders are generally mounted in the upper edge area of the windshield in the area covered by the interior rear view mirror. This area is quite small and not well suited to accommodating antennas for a plurality of radio services having various frequencies. However, the possibilities of mounting antennas at other locations in the motor vehicle are also limited because placing them under the metallic skin of the vehicle is impossible in principle.
It is an object of the present invention to use a vehicle navigational radio service and a telematic radio service, while making economical use of the space available for mounting antennas on the vehicle surface.
This object may be achieved in accordance with the present invention by mounting a second planar antenna for receiving a telematic radio signal so that it at least partially overlaps the first antenna, and connecting it to a second signal processing circuit. The antennas and the associated signal processing circuits are thus joined to form a combined module, whose space requirements on the vehicle surface are not greater, or at most only slightly greater, than those of the larger of the individual antennas.
The two planar antennas, specifically, microstrip antennas, may include patches, that are separated from each other by a first dielectric and are separated from a common ground plane (area) by a second dielectric, the dielectric constants of the dielectrics being different and the patch for the higher-frequency radio signal bordering on the dielectric having the lower constant, and the patch for the lower-frequency radio signal bordering on the dielectric having the higher constant.
In conventional microstrip antennas, the resonance frequency is determined, on the one hand, by the dimensions of the microstrip antenna itself and, on the other hand, by the dielectric constants of a material that separates the microstrip antennas from a ground plane arranged opposite. The higher this dielectric constant is, the smaller the microstrip antenna may be, assuming the identical resonance frequency. The assignment of dielectrics to the antennas makes it possible to reduce the dimensions of the antenna assigned to the lower-frequency signal and to make them approximate those of the other antenna, thus ultimately making for a compact configuration of the antenna set-up.
For purposes of manufacturing, the patches of the two antennas may be arranged in parallel planes.
Due to the diversity in the operating frequencies of the radio services in question and of the two antennas, it is possible to connect the processing circuits to the patches using one common supply line.
However, in order to avoid overcoupling between the signals of the different radio services, each patch may be connected to the assigned processing circuit by its own supply line.
This may be achieved by routing the supply line of the exterior of the two patches through an opening in the other one, arranged between the exterior patch and the ground plane.
According to one exemplary embodiment, the two planar antennas each have different main transmitting directions. A differentiation of this type in the main transmitting directions reflects the individual application situation of the two radio signals. Whereas GPS radio signals arrive on average from the zenithal direction, telematic signals are generally received at changing angles of elevation in an angular range that is centered around the direction of motion of the vehicle. Therefore, it is useful if the antenna for the navigational signal is aligned to the vertical, while the antenna for the telematic signal is aligned to the direction of motion of the vehicle.
A differentiation of this type may be achieved in that the centroids of the patches of the two antennas, as projected onto the ground plane, are offset with regard to each other.
To achieve the desired orientation of the main transmitting direction, it is useful if the installation position is oriented such that the link between the projected centroids extend in the direction of the strongest gradient of the ground plane, in other words, the orientations of the patches are selected so that their surface normals lie between the expected average directions of incidence of the navigational radio signal and of the telematic radio signal.
In addition, it is useful if the patch of the second planar antenna, assigned to the telematic radio signal, is arranged in a plane between the patch of the first planar antenna and the ground plane. In this manner, the reception of the navigational signals, originating from very distant satellites and having limited transmission power, is not impaired by the antenna for the telematic radio signal; damping the reception of this signal by the first planar antenna may be tolerated much better, because, in the case of most telematic applications, the vehicle passes at a short distance to a transmitter of the telematic radio signal. Thus, the telematic radio signal in any case is received at a high level of dynamic response, and any deficit in the reception level that may arise may be equalized much more easily, by slightly increasing the transmission power, than in the case of navigational radio signals.
To connect the module to a motor vehicle electronics, a common connector may be used, through which navigational and telematic signals are transmitted in different frequency ranges. This facilitates the integrated processing of telematic navigational signals, e.g., calculating tolls on the basis of data from the navigational system.
Control signals for switching the processing circuit of the telematic radio signal between the transmitting and receiving modes may be sent in a further frequency range via this connector.
Finally, a DC component of a signal that is fed from outside to the connector is well suited for supplying power to the signal processing circuit of the module.
All of these signals may be conveniently conveyed over one single coaxial cable, for which reason the connector may be configured as a coaxial connector.